1. Field of the Invention
The present invention relates to a device for operating a charge transfer device such as a charge couple device (CCD).
2. Description of the Related Art
Conventionally, a device for operating the charge transfer device includes a driver for outputting control signals by which the charge transfer device is operated, and a power supply circuit for applying a voltage to the driver. In the charge transfer device, a vertical transfer CCD transfers electric charges accumulated on photodiodes to a horizontal transfer CCD or a discharge drain. The electric charge transferred to the horizontal transfer CCD is transferred to a floating diffusion amplifier and changed to a voltage to be outputted as a video signal, while an unwanted electric charge is transferred to the discharge drain.
When an electronic shutter is operated, for example, only electric charges accumulated on the photodiodes during a predetermined period must be transferred from the vertical transfer CCD to the horizontal transfer CCD to form a picture or image. Therefore, electric charges accumulated during a period other than the predetermined period must be discharged from the vertical transfer CCD to the discharge drain. This discharge operation of the vertical transfer CCD must be carried out at a high speed so that the image-forming operation is not interrupted.
Nevertheless, since a large amount of electric current flows between the driver and the vertical transfer CCD when the vertical transfer CCD is operated at a high speed, a relative drop occurs in the voltage supplied to the driver. As a result, unwanted electric charges are not fully discharged to the discharge drain. Therefore, residual electric charges are superposed on electric charges corresponding to an original image. Thus, the image quality is lowered. Such a voltage change can be prevented by providing a capacitor having a large capacity, but this increases the size of the circuit.